In extracorporeal blood processing, blood is taken out of a human or animal subject, processed in a dialyzer and then reintroduced into the subject by means of an extracorporeal blood flow circuit. Such extracorporeal blood processing includes hemodialysis, hemodiafiltration, hemofiltration, ultrafiltration (fluid removal), etc.
Generally, the extracorporeal blood processing is aimed at achieving movement of water and solutes across a semi-permeable membrane inside the dialyzer. In many types of extracorporeal processing, this is achieved by pumping the blood through the dialyzer on one side of the semi-permeable membrane and by pumping a treatment solution (dialysis fluid) through the dialyzer on the other side of the semi-permeable membrane.
Prior art dialysis systems comprise a complex supply arrangement for preparing and conditioning the treatment solution and for pumping the treatment solution through the dialyzer. The supply arrangement defines a fluid path which extends through a number of separate components such as pumps, valves, connectors, fluid lines, sensors, ultrafiltration measurement devices, etc. The manufacturing of such a supply arrangement is labor intensive. Also large number of connections and detachable and movable parts may lead to leakage of fluid and/or operational failure and need for maintenance.
US2012/0106289 discloses a plurality of separate cassettes that may be implemented to form functionally different parts of a supply arrangement for treatment solution in a dialysis system. A mixing cassette is implemented to mix the treatment solution and then send the treatment solution to a storing vessel or reservoir. A middle cassette is implemented to provide fluid lines and ports. A balancing cassette is implemented with balancing chambers for balancing the volume of fluid that enters the balancing cassette in one direction with the volume of fluid that enters the balancing cassette from another direction. The balancing cassette is also implemented to provide a metering function where a volume of fluid from one direction may be pumped such that it bypasses the balancing chambers and does not affect the balancing volumes. The cassettes may be combined into a cassette device/system that mixes treatment fluid, transports treatment fluid and balances the volume of treatment fluid before and after flowing through a dialyzer. Each cassette contains at least one reciprocating positive-displacement pump, denoted “pod pump”. Each pod pump is formed by an essentially spherical interior cavity containing a flexible membrane that effectively divides the spherical cavity into a variable-volume pumping chamber and a complementary variable-volume actuation chamber. The actuation chamber as well as valves associated with the pod pump are pneumatically controlled. The membrane is urged to move back and forth within the cavity by alternately applying, to the actuation chamber, negative pneumatic (or atmospheric) pressure and positive pneumatic pressure. Valves at a fluid inlet and a fluid outlet of the pumping chamber are operated in synchronization with the reciprocating membrane to cause treatment fluid to be pumped through the pumping chamber. Each valve may be controlled to open and close by pneumatic pressure acting on a membrane which is installed in the cassette to cooperate with a respective valve seat. Each cassette is formed as an assembly of three plates that are formed with complementary channels to define the interior cavities of the pod pumps as well as appropriate paths for pneumatic pressure and treatment solution. To form the pod pumps and the valves, separate membranes are fitted between at least two of the plates. A similar hemodialysis system is shown in WO2008/106191.
The supply arrangements of US2012/0106289 and WO2008/106191 include several cassettes and many separate parts to be assembled in production. Thus, manufacture is complex and the supply arrangement has many points of failure as well as many connections that may cause leakage. It is realized that a failure in a moving component inside one of the cassettes results in rejection of the entire cassette, or even the entire cassette system, since it may be difficult or impossible to open the cassette to replace the failing component. Furthermore, the provision of plural membranes inside the cassette constrains the design of the cassettes and may result in an increased form factor.
In the field of peritoneal dialysis (PD), it also known to provide a disposable cassette for installation in a PD cycler for the purpose of supplying a treatment fluid. The cassette is a unitary component formed of a rigid base body or frame which defines interior cavities, and a coherent diaphragm, foil or sheeting that overlies the entire body or frame and its cavities to define pump stations, fluid paths and valve stations inside the cassette. The cassette is mounted in the cycler to interface with an actuator system which acts on the diaphragm, foil or sheeting to impart a desired movement to a treatment fluid through the cassette. The actuator system may operate to apply localized positive or negative pneumatic pressures at the diaphragm, foil or sheeting, as shown in WO94/20158, WO2009/094182, WO2009/094183 and US2009/0012455, or by operating a reciprocating piston to act on the diaphragm, foil or sheeting, as shown in US2011/0196289 and US2012/0259276.
The use of disposable cassettes for supplying blood in a blood processing apparatus is disclosed in WO01/17584, WO01/17649 and WO03/101510. These disposable cassettes also consist of a rigid base body with fitted chambers and passages and a foil or diaphragm covering them. The cassettes are mounted in a control station of the blood processing apparatus, which applies a varying pneumatic or hydraulic pressure on the foil or diaphragm to pump the blood through the cassette. The prior art also comprises so-called fluidic pumping systems in which alternating negative and positive gas pressure acts directly on a liquid in a chamber to pump the liquid through the chamber. US2006/0196884 proposes such a pumping system for bulk fluid distribution in manufacture of semiconductor devices. GB2283065 discloses a fluidic pumping system for pumping of radioactive or hazardous liquids. Another fluidic pumping system is known from GB2239904.
Even if fluidic pumping systems are known as such, the prior art does not suggest the use of these fluidic pumping systems in medical systems in general, let alone for pumping of treatment solution in dialysis systems. Nor does the prior art suggest that these fluidic pumping systems could be integrated in cassettes or bonded manifolds. In fact, the prior art consistently teaches that cassettes for pumping a treatment solution through a dialyzer should include diaphragms, membranes or foils that are actuated to impart a desired movement to the treatment fluid through the cassette.